Fabricating a chip, which starts with a bare wafer of silicon, may involve hundreds of different processes. One of the most fundamental steps in the manufacturing process is impregnating flawless silicon with intentional abnormalities, around which the structure of the chip will eventually be built. This process is called ion implantation and is an incredibly complex mix of high-energy physics, molecular chemistry, and robotics. As the size of the channels on chips continues to get smaller, the art of implanting ions gets even more complicated.
The process of implanting ions involves delivering a beam across the wafer, often at different angles to achieve desired geometries. Providing a uniform beam angle across the wafer is critical for eliminating unwanted effects. Challenges arise however because different parts of the beam hit different parts of the wafer. Further difficulties arise because when a beam is directed at a wafer at a non-zero angle, the photo-resist material on the surface of the wafer will block, i.e., “shadow,” the beam, so that only one wall within a trench is actually implanted. Accordingly, techniques are required that will both average out the effects of the beam and address shadowing.
A common approach for addressing these issues includes utilizing a conventional quad mode implant that will vary the wafer rotation. Quad mode involves repositioning the wafer four times by rotating it 90 degrees. By rotating the wafer to four different positions, four different walls within a trench can be separately implanted. However, since each step of the quad mode is actually doping a different part of the wafer, the rotation does not accomplish any averaging (i.e., uniformity). Another approach is to tilt the wafer about a single axis to provide different beam angles for implanting different walls. Similarly, this approach fails to provide uniformity. Accordingly, a need exists for an improved system and method of implanting ions that will reduce the effect of beam imperfections.